1. Field of the Invention
The present invention relates to a rotary pin, and more particularly, to the structure of a pin having a grease hole that is rotatably supported to a bearing.
2. Description of the Related Art
In FIG. 7, part of a rear axle of a forklift is shown. A cylinder rod 5 of a cylinder 4 is coupled through a tie rod 3 to a knuckle arm 2 formed onto an axle shaft of a steering wheel 1. The knuckle arm 2 and the tie rod 3, and the tie rod 3 and the cylinder rod 5 are rotatably coupled to a rotary pin 6 and a rotary pin 7, respectively, and the steering wheel 1 rotates about a king pin 8 through the tie rod 3 and the knuckle arm 2 in accordance with expansion and contraction of the cylinder rod 5.
In FIG. 8, the rotary pin 7 that couples the tie rod 3 to the cylinder rod 5 is shown. The rotary pin 7 has an eccentric portion 9a that is rotatably supported to a bearing of the tie rod 3. When the rotary pin 7 is rotated about an axis thereof with respect to the cylinder rod 5, the eccentric portion 9a rotates about the central axis of the rotary pin 7. Accordingly, a relative position of the tie rod 3 to the cylinder rod 5 changes in accordance with its rotational angle. As a result, fine adjustment of a steering angle of the steering wheel 1 is performed.
It is arranged such that each time the cylinder rod 5 is expanded or contracted to control the steering wheel 1, the tie rod 3 rotates about the eccentric portion 9a of the rotary pin 7. Therefore, in order to improve lubricity between the eccentric portion 9a of the rotary pin 7 and the bearing of the tie rod 3, and in order to prevent abrasion of contact surfaces thereof, a grease hole 10a is formed in the rotary pin 7 from a top end thereof. The grease hole 10a is open on an outer circumferential surface of the eccentric portion 9a, so that grease can be injected onto the outer circumferential surface of the eccentric portion 9a from the top of the rotary pin 7 through the grease hole 10a. 
Conventionally, however, as shown in FIG. 8, the grease hole 10a has been open at both ends of one diameter at the central portion in an axial direction of the eccentric portion 9a. Accordingly, the grease hole 10a penetrates a section on which the maximum load acts at the movement between the tie rod 3 and the cylinder rod 5, with the result that a problem arise in which the strength of the rotary pin 7 is lowered. Therefore, there was an anxiety that product life of the rotary pin 7 was shortened, for example, when an excessive impact force was applied to the steering wheel 1 or the like from outside.
Next, the rotary pin 6 that couples the knuckle arm 2 to the tie rod 3 is shown in FIG. 9. The rotary pin 6 has a spherical portion 9b that is rotatably supported to a bearing of the knuckle arm 2. It is arranged such that each time the cylinder rod 5 is expanded or contracted to control the steering wheel 1, the knuckle arm 2 rotates about the spherical portion 9b of the rotary pin 6. Therefore, in order to improve lubricity between the spherical portion 9b of the rotary pin 6 and the bearing of the knuckle arm 2, and in order to prevent abrasion of contact surfaces thereof, a grease hole 10b is formed in the rotary pin 6 from a top end thereof. The grease hole 10b is open on the outer circumferential surface of the spherical portion 9b, so that grease can be injected onto the outer circumferential surface of the spherical portion 9b from the top of the rotary pin 6 through the grease hole 10b. 
As shown in FIG. 9, however, the grease hole 10b has been merely open at the central portions of the spherical portion 9b in the axial direction. Accordingly, it was difficult to inject grease uniformly over the outer circumferential surface of the spherical portion 9b, with the result that a problem arose in which grease was consumed rapidly in a short period of time.
The present invention was made to solve these problems, and it is an object of the present invention to provide a rotary pin in which grease can be injected onto a contact surface in contact with a bearing while keeping a required strength.
Further, it is another object of the present invention to provide a rotary pin in which grease can be injected uniformly onto the contact surface in contact with the bearing and it is possible to make grease last for a long period of time.
According to a first aspect of the present invention, there is provided a rotary pin rotatably supported to a bearing comprises:
a rotary pin main body; and a contact surface positioned at an outer circumferential portion of the rotary pin main body for being in contact with the bearing, a grease hole extending from one end of the rotary pin main body in an axial direction thereof, and a plurality of grease injection holes open on the contact surface so as to be axially separated on both sides from a central portion of the contact surface being communicated with the grease hole, respectively.
It is preferable that the plurality of grease injection holes are arranged so as to be axially separated on both sides from the central portion of the contact surface by L/4 when L is a length of the contact surface in the axial direction thereof. Furthermore, it is preferable that a pair of grease injection holes are arranged so as to be axially separated on both sides from the central portion of the contact surface and faced with each other in opposite directions. Or, it is preferable that four grease injection holes are formed respectively at both ends of a pair of diameters arranged in parallel with each other so as to be axially separated on both sides from the central portion of the contact surface. Further, a grease injection hole arranged at a position near the one end of the rotary pin main body may have a diameter smaller than that of a grease injection hole arranged at a position far from the one end of the rotary pin main body.
Further, four grease injection holes may be formed respectively at both ends of a pair of diameters arranged in orthogonal with each other so as to be axially separated on both sides from the central portion of the contact surface. The rotary pin may be a spherical pin having the contact surface convex toward outside. It is preferable that an edge portion of each grease injection hole is chamfered. The contact surface may be an outer circumference of an eccentric portion off-centered from a central axis of the rotary pin main body.
According to a second aspect of the present invention, there is provided a rotary pin having a spherical portion rotatably supported to a bearing comprises: a rotary pin main body; and a spherical portion positioned at an outer circumferential portion of the rotary pin main body for being in contact with the bearing, a grease hole extending from one end of the rotary pin main body in an axial direction thereof, at least one grease injection hole open on the outer circumferential surface of the spherical portion being communicated with the grease hole, at least one vertical grove which extends in an axial direction of the rotary pin main body for retaining grease and stirring grease being formed on the outer circumferential surface of the spherical portion.
A pair of grease injection holes may be formed at both ends of one diameter of the spherical portion that is orthogonal to the central axis of the rotary pin main body; and a pair of vertical groves may be formed at potions orthogonal to the pair of grease injection holes about a central axis of the rotary pin main body. A vertical grove may be formed so as to overlap with each grease injection hole. The plurality of grease injection holes may be arranged so as to be axially separated on both sides from the central portion of the spherical portion. The spherical portion may be off-centered from a central axis of the rotary pin main body.